Electric submersible pump (ESP) systems are typically installed in oil and gas wells where reservoir pressure is inadequate to lift reservoir fluids to the surface or to increase production in natural producing wells. As a reservoir is produced, the pressure in the pore space of the rocks decreases, and thus may require the introduction of some type of artificial lift system to continue production as a reservoir or a well ages. An ESP system provides an artificial lift for a reservoir and/or well and comprises a motor to convert electrical power from a cable to mechanical power to drive the pump.
When using an ESP system, a production tube with a power line attached is typically installed into a completed well so that one or more powered device of the ESP system can be connected to the power line for a number of purposes. It is advantageous to use a remote electrical connection means (also known as a wet connector or wet connect) which permits, among other things, the removal of the powered device for replacement or repair without the necessity to remove the production tube and power line each time. Connection of a powered device to the installed power line via a wet connector may be designed to take place at any point along the length of the well but is typically positioned at the lower or furthest end of the well.
The wet connector is a sensitive electromechanical device and is arranged at the lower end of the production tube and is usually installed with the powered device to form a bottom hole assembly (BHA). This BHA is prone to damage and/or debris agglomeration during installation, particularly when deployed into a deviated or horizontal well. The wet connector arrangement typically requires a plug arm protruding into a window in the production tubing to enable it to be selectively electrically connected to the power line. This window increases the vulnerability of the wet connector as it is prone to permit access for an increase of debris accumulation in the vicinity of the wet connector.
Accordingly, when utilizing such a BHA it is useful to have reliable and accurate information concerning the position and orientation of any downhole equipment during and after installation. It is particularly important to have information about the orientation of the BHA to ensure the orientation reflects the configuration that is most reliable and least open to contaminants during operation such as pumping when it may be exposed to substantial fluid and debris movement. Sand and other debris can be produced along with the oil and gas during production. Often debris and sand will accumulate at the BHA and can damage the wet connector or will prevent the electrical connector from properly mating. Debris that is present at any point in the well may potentially damage or interfere with the mating of the connector. This debris may consist of moisture in addition to sand and grit. These substances can quite easily accumulate in the exposed orifices of the BHA, and particularly near the electrical connections of the wet connect for the supply of power to the downhole powered device. The accumulation of sand, grit and oil can cause severe disruption to the activity of the electrically powered device and may increase the likelihood of failure. The increased likelihood of disruption creates a reasonable incentive to best ensure the most reliable orientation of the BHA.
Because there is an increased accumulation of debris at the lowest point of the bore, it is preferential to orient the BHA to direct all vulnerable orifices and electrical connections upward. In the past, techniques have been developed to achieve a particular orientation of downhole completion components, including gravity oriented systems (weights), mechanically ‘scribed’ orientation, mule shoes (and various other mechanical placement devices) and later measurement runs on wireline to measure (and subsequently correct) the orientation of the installed completion. One such orienting technique is a process called scribing. In this process, a ‘scribe line’ is made down the length of the tubing in a known orientation. The line can be marked on the tubing as part of the manufacturing process or can be made on the rig as the tubing is being installed. As each tubing joint is assembled the scribe line is carefully monitored to keep track of the orientation of the scribe line at the bottom of the tubing string. As the bottom of the tubing string approaches the final depth setting the tubing string is rotated at the surface to place the scribe line in the correct position to orient the completion in the desired direction. This method is simple and inexpensive but the accuracy is poor and the opportunity for an error is very high, as small errors can accumulate and become large ones.
Other known techniques include orientation guides, mule shoes and other mechanical devices. A number of such mechanical devices have been developed that orient the tubing string as it is installed into the casing. A typical system is shown by EP 0872626. These systems have the advantage that they positively locate the tubing string axially and orient with a reliable mechanical connection. One disadvantage associated with the use of these systems is that installation of a mule shoe or other orienting device is required prior to running the casing or as a subsequent operation. Once installed, the mule shoe or orienting device may obstruct all or much of the annular space available, and the tubing or the device being oriented can become stuck in the mule shoe or its accompanying locking system. Therefore, any advance that could provide for a more reliable and protected manner of downhole orientation for ESP system components would provide a competitive advantage.